The invention relates to a powder-feeding system for gas-propelled delivery of a powder to be controllably supplied, as to a flame-spraying gas torch or to a transferred-arc plasma torch.
Various schemes have been proposed for the aspiration of powder into a flow of carrier gas, but these have lacked the precision with which it is desirable to controllably meter the delivery of powder to a torch for torch deposition to a surface to be coated or otherwise treated by the powder.
U.S. Pat. No. 3,976,332 attacks the problem by so configuring a downwardly open orifice in a carrier-gas tube within the convergent lower region of a powder-supply hopper that, in the presence of a fluidizing-gas flow from the top of the hopper and through the body of powder in the hopper, a fluidized powder regime will be established in the immediate vicinity of the orifice, thereby providing fluidized powder under pressure for conveyance by the carrier-gas flow. This technique has the disadvantage that the pressure drop of fluidizing-gas must necessarily be some function of the instantaneous head of undischarged powder within the hopper. And the the patentee discloses a vibrator on the hopper wall as an aid in agitating undischarged powder in order to reduce this pressure drop.